Method for forming flash holes in cartridge cases

ABSTRACT

A method of forming flash holes in cartridge shells wherein the holes are impact punched rather than drilled. It has been discovered that these holes can be impact punched where the shell metal has a difference of at least 5 percent between its yield strength and its ultimate tensile strength, with an attendant substantial saving in time and cost over drilling.

United States Patent Otto E. Reider Etobicoke, Ontario, Canada 829,280

June 2, 1969 May 25, 1971 General Impact Extrusions (Manufacturing) Ltd. Toronto, Ontario, Canada Inventor Appl. No, Filed Patented Assignee METHOD FOR FORMING FLASH HOLES IN CARTRIDGE CASES 6 Claims, 4 Drawing Figs.

US. Cl 29/13, 29/558, 83/194 Int. Cl B23p 15/22 Field of Search... 29/ 1 .3,

1.31, 1.32, 564,558; 83/194, 193; 86/(lnquired); 102/(lnquired); 77/(lnquired) {5 6] References Cited UNITED STATES PATENTS 1,503,551 8/1924 Nice 83/193X 2,315,340 3/1943 Knudsen 83/193X 2,325,437 7/1943 Temple 83/194 2,423,791 7/1947 Nelson 83/194X Primary Examiner-Frank T. Yost Attorney-Fetherstonhaugh and C0.

PATENTEU was IHYI SHEU 1 BF 2 Flea ATTORNEYS PATENTEU M2519?! SHEET 2 OF 2 ATTORNEYS METHOD FOR FORMING FLASH HOLES IN CARTRIDGE CASES This invention relates to the manufacture of cartridge cases and is particularly concerned with a method for forming flash holes in dual pressure cartridge cases.

In a normal single pressure cartridge, the powder is located between the primer positioned at the rear end of the cartridge and the projectile. In a dual pressure cartridge, the powder is contained in a hollow boss on the inside of the rear wall of the cartridge. The annular wall of the boss is provided with a number of holes through which pass the high pressure gases resulting from ignition of the powder. These holes, which are known as flash holes, are designed to let out the high pressure gases at a controlled rate. The gases exit into a lower pressure cavity consisting of the annular space surrounding the outside wall of the boss and the inside wall of the cartridge case, and between the rear wall of the cartridge and the projectile.

In the manufacture of dual pressure cartridges, a blank is forged into a preform which essentially consists of a disc having the aforementioned boss which is positioned at the center of the disc. Subsequently, the outer rim of the disclike preform is folded upwardly around the boss to define the outer wall of the cartridge. However, prior to the upward folding of the cartridge wall, the flash holes are formed through the annular wall of the boss. I

Heretofore the only known method for placing the holes in the wall of the boss has been to drill them, using high speed drills. This is a time-consuming and expensive process, but it was the only one available which could produce flash holes of small diameter through the relatively thick walls of the boss.

It is, therefore, an object of this invention to provide an improved method for forming flash holes in dual pressure cartridge cases.

It is a more specific object of the invention to provide a method as above defined which is faster and less expensive than the known method of using high speed drills.

In accordance with the present invention, the above objects are gained by the impact punching of the flash holes, with all of the holes being formed simultaneously and at the same speed so that the forces counteracting on the punches are in equilibrium. The method is surprising in that it is capable of forming flash holes which are as much as twice as deep as the diameter of the punches used, even though it is normally believed that it is not possible to produce holes in relatively hard materials which are greater in depth than the diameter of the punch.

The invention will be more thoroughly understood from the following description of a preferred method for carrying it out, reference being made to the drawings.

In the drawings:

FIG. 1 is a perspective view, partially broken away, of a preform blank forged cartridge casing for a 40 mm. shell;

FIG. 2 is a side elevation view, partly in section, of a preferred apparatus for carrying out the flash hole forming method of the invention;

FIG. 3 is a cross-sectional view of the preform blank of FIG. I after punching of the flash holes and upward folding of the cartridge wall; and

FIG. 4 is a perspective view, partly broken away, of the preform blank of FIG. 1 in its finished condition.

It should be understood that the shell is illustrated in the drawings only as one example of the type of dual pressure cartridge which requires the formation of flash holes 11 through the wall of the central boss I2 and leading to the lower pressure cavity 13 surrounding the boss. As previously mentioned, prior to the present invention, the only known method for forming flash holes was to use high speed drills.

In accordance with the present invention, the holes are formed by punching, with all of the holes being formed at the same time and with all of the punches being moved against the wall of the boss at the same speed. A surprising feature of the flash-hole forming method of the invention is that punched holes can be formed in casing walls of a thickness greater than the diameter of the punches. As a matter of fact, the flash holes formed in the casing walls for 40 mm. shells are approximately twice as great in depth than the diameter of the punches used, It has also been found that the method can produce tapered holes.

The method of the invention can be used on all wrought metals or malleable metals, such as brass, copper, aluminum, zinc, steel and titanium, provided there is a difference of at least 5 percent between its yield strength and its ultimate tensile strength. The method works best when this difference is 10 percent or more. It is essential, of course, that the compression strength of the material used in the punches exceeds the compression strength of the workpiece material. It is preferable that the compression strength of the punches material exceeds that of the workpiece material by a factor of 1.2.

In forming flash holes in cartridges formed of most aluminum alloys, it is possible to form the holes by a single punching step. However, for cartridge materials of a different composition, it might be necessary to form the holes by a number of impacts and the method is adapted to such a modification. It is not necessary that the punches be in contact with the workpiece at all times so that a number of punching movements can be performed where it is advantageous to do so and where it is necessary to introduce a lubricant between the punches and the workpiece. The method is also adapted to the use of sonic or ultrasonic vibration along the length axis of the punches over the forming pressure where this is necessary or desirable, depending upon the nature of the material of which the cartridges are formed. It has been found that the free length of the punch shanks can be increased or the punch load reduced by the use of such sonic or ultrasonic vibrations.

The apparatus illustratedin FIG. 2 is an example of the type of equipment that can be used to carry out the flash hole forming method of the invention. The illustrated apparatus essentially consists of a plurality of punches arranged to surround a cartridge shell and includes that equipment which is necessary to move all of the punches-simultaneously against the outside of the boss with the same impact force in each case.

The punches shown in FIG. 2 are those that are used in the forming of flash holes in the previously mentioned 40 mm. aluminum alloy cartridge case. The preferred included angle at the punch face for forming holes in this particular material is 136 but satisfactory holes can be formed by using higher pressures with punched faces having included angles of from l (flat) to conical. The particular punched configuration selected for forming holes in any particular cartridge case depends, of course, on the composition of the metal of which the case is formed.

REferring now to FIG. 2, the illustrated apparatus will not be described in detail. The workpiece involved is a preformed blank 10 of the type shown in FIG. I. The preform is impact forged from a slug of aluminum alloy and includes a central boss 12 and a central cavity 14, it being the object of the invention to produce, by punching, flash holes extending from the cavity through the wall of the base.

The illustrated apparatus essentially consists of a lower die 16, an upper die 18 and a plurality of punches 20 carried by the upper die. Only two punches are shown and, while the invention could be carried out on shells requiring only two flash holes, it is the normal practice to provide six or more flash holes which are evenly spaced from one another around the circumference of the-boss. In the interest of simplicity, however, the mechanisms which achieve the forward movement and retraction of only a single punch are described hereinafter, but it should be understood that such mechanisms are provided for each punch so that the apparatus as a whole, when viewed from above, has the appearance of a spoked wheel, i.e., with a number of punched moving mechanisms arranged around a central hub at which the preformed blank is held.

Each punch 20 is held within and is capable of reciprocation within its own longitudinal cavity 22 in the upper die 18. At its other end, the punch is held by block member 26 which is capable of sliding on a guide member 24. The outer edge of block 26 is sloped surface of a vertically oriented fixed member 30. T It can be seen, therefore, that as upper die 18 moves downwardly, block 26 is forced inwardly by the cam reaction between pad 28 and the sloping surface of upright 30. It is this inward forcing of block 26 and punch 20 which produces the desired flash hole through the wall of boss 12. For retraction, block 26 carries another sloping face which bears against a reverse slope on the other side of upright 30.

In operation, the preformed blanks are manually or automatically fed onto the top surface of lower die 16, at which point the die 16 is in a lowered position so that the preform is at the level shown in dotted lines when first fed onto the top surface of die 16. Die 16 is then raised until the preform is tightly clamped between the dies. When this clamping action takes place, the upper die 18 is actually in a position higher than the position shown in FIG. 2. In fact, upper die 18 is at a level which is reached when it has been fully raised to retract the punches from the previous preform blank.

Following the raising of the lower die 16 as to clamp the preform blank between the dies, the dies and the blank are moved down together at which stage the interaction of the sliding blocks 26 with the uprights 30 causes each of the punches to move inwardly against the boss 12 as to simultaneously punch the desired flash holes. Finally, the upper die [8 is raised until the punches are fully retracted and then raised a little further so that the preformed blank bears against the lower end of an ejector rod 32 so that the blank is caused to drop out of the upper die. Simultaneously, with the raising of the upper die to retract the punches, the lower die 16 is dropped downwardly into its lowermost position in readiness to receive the next preformed blank.

In summary, therefore, the sequence is the feeding of a preformed blank onto the top surface of lower die 16, the raising of die 16 as to clamp the preformed blank between the dies, the lowering, en masse, of the two dies and the clamped blank during which stage the punching operation takes place, and finally the raising and lowering of the upper and lower dies respectively, accompanied by ejection ejection of the blank which now carries the desired flash holes.

Following the punching operation carried out by the apparatus of FIG. 2, the blank is subsequently reworked to upwardly fold the cartridge wall until the blank takes the form shown in FIG. 3. This particular operation does not differ from the same operation that has been carried out on this type of cartridge casing known heretofore, it being understood that the present invention primarily relates to the impact punching of the flash holes as contrasted with the former method of drilling these holes. However, it should be noted that the inner end of cavity 14 has a somewhat different form following the punching operation than the form shown in FIG. 1. This change in form of the lower end of cavity 14 is a direct result of the punching operation as the boss material adjacent the inner end of the cavity is caused to flow into the cavity. Indeed, it is the earlier provision of cavity 14 which provides a space for the boss material to flow into which permits the impact punching of holes which are much greater in depth than their own diameter. Heretofore the punching of such holes in the relatively hard materials of which cartridge cases are made was thought impossible.

As a final step, cavity 14 is reamed out and extended in depth so that the final size of the hole is equivalent to the dotted line configuration shown in FIG. 3. As it is normal to effect the final reaming of the cavity, even in the previous method of forming flash holes by drilling, no extra time or effort is involved in carrying out this final reaming step.

The final form of the cartridge is shown in FIG. 4, but the additional work required to complete the cartridge involves steps which are carried out in any case and do not relate to the present invention.

It should be appreciated that dual pressure cartridge cases are manufactured in very high volumes so that the flash hole fonnrng method of the invention effects considerable savings in cost over the only known method of forming these holes by drilling. It should also be understood that the holes formed by the impact punching method of the invention are better than those produced by drilling in that much less material is removed from the cartridge walls.

Iclaim:

l. A method of forming flash holes in dual pressure cartridge shells of the type wherein the shells are formed of a metal having a difference of at least 5 percent between its yield strength and its ultimate tensile strength, comprising the steps of holding the cartridge casing in a fixed position and impact punching blind flash holes to cause metal to blow and bulge the configuration of the cartridge casing, the punching operations all being carried out at the same time and at the same speed so that the forces counteracting the punching processes are in equilibrium and reaming a cavity in the cartridge casing that intersects the inner ends of said flash holes whereby said flash holes become through holes.

2. A method of forming flash holes through the wall of the boss of a dual pressure cartridge formed of a metal having a difference between its yield strength and its ultimate tensile strength of at least 5 percent, comprising the steps of taking a cartridge preform consisting of a disc which includes a central boss having a central cavity whereby the outside surface of the boss and the cavity define a tubelike boss wall, positioning a plurality of punches around the boss with the longitudinal axis of the punches lying substantially normal to the boss wall and with the punches equally spaced from one another, forcibly driving said punches into said boss wall, to form a blind hole and cause metal to blow and bulge the configuration of said central cavity, all of said punches being moved at substantially the same rate of speed at substantially the same force, and enlarging said cavity to remove therefrom such cartridge materia] as has flowed into said cavity during the punching operation, and include the inner ends of said flash holes whereby said flash holes become through holes.

3. A method as claimed in claim 2, in which said punches are driven into said boss wall in one stroke.

4. A method as claimed in claim 2, in which said punches are drawn into said boss wall by a plurality of advancing strokes.

5. An apparatus for preliminarily forming flash holes through the wall of the boss of a dual pressure cartridge formed of a metal having a difference between its yield strength and its ultimate yield strength of at least 5 percent, said apparatus consisting of a first die member for holding a disclike cartridge preform having a central boss which includes a central cavity, the preform being held with the boss projecting outwardly of said first die member, a second die member, means for moving said die members together as to clamp said preform between said die members with said boss being held within said second die member, block members carried by said second die member on guide elements and adapted for radially directed sliding movement on said guide elements, a punch carried by each of said block members on the inside thereof and directed towards the outside surface of said boss, a plurality of fixed elements carrying sloped camming surfaces positioned adjacent said block members, and camming surfaces carried by said block members and in contact with the camming surfaces on said fixed elements whereby a first movement of said die members and the contained preform relative to said fixed elements will drive said punches into the wall of said boss causing flow of metal into said cavity which may subsequently be reamed out and whereby a second reverse movement of said die members and said preform will retract said punches.

6. An apparatus as claimed in claim 5, further including punch guiding passageways carried by said second die member. 

1. A method of forming flash holes in dual pressure cartridge shells of the type wherein the shells are formed of a metal having a difference of at least 5 percent between its yield strength and its ultimate tensile strength, comprising the steps of holding the cartridge casing in a fixed position and impact punching blind flash holes to cause metal to blow and bulge the configuration of the cartridge casing, the punching operations all being carried out at the same time and at the same speed so that the forces counteracting the punching processes are in equilibrium and reaming a cavity in the cartridge casing that intersects the inner ends of said flash holes whereby said flash holes become through holes.
 2. A method of forming flash holes through the wall of the boss of a dual pressure cartridge formed of a metal having a difference between its yield strength and its ultimate tensile strength of at least 5 percent, comprising the steps of taking a cartridge preform consisting of a disc which includes a central boss having a central cavity whereby the outside surface of the boss and the cavity define a tubelike boss wall, positioning a plurality of punches around the boss with the longitudinal axis of the punches lying substantially normal to the boss wall and with the punches equally spaced from one another, forcibly driving said punches into said boss wall, to form a blind hole and cause metal to blow and bulge the configuration of said central cavity, all of said punches being moved at substantially the same rate of speed at substantially the same force, and enlarging said cavity to remove therefrom such cartridge material as has flowed into said cavity during the punching operation, and include the inner ends of said flash holes whereby said flash holes become through holes.
 3. A method as claimed in claim 2, in which said punches are driven into said boss wall in one stroke.
 4. A method as claimed in claim 2, in which said puNches are drawn into said boss wall by a plurality of advancing strokes.
 5. An apparatus for preliminarily forming flash holes through the wall of the boss of a dual pressure cartridge formed of a metal having a difference between its yield strength and its ultimate yield strength of at least 5 percent, said apparatus consisting of a first die member for holding a disclike cartridge preform having a central boss which includes a central cavity, the preform being held with the boss projecting outwardly of said first die member, a second die member, means for moving said die members together as to clamp said preform between said die members with said boss being held within said second die member, block members carried by said second die member on guide elements and adapted for radially directed sliding movement on said guide elements, a punch carried by each of said block members on the inside thereof and directed towards the outside surface of said boss, a plurality of fixed elements carrying sloped camming surfaces positioned adjacent said block members, and camming surfaces carried by said block members and in contact with the camming surfaces on said fixed elements whereby a first movement of said die members and the contained preform relative to said fixed elements will drive said punches into the wall of said boss causing flow of metal into said cavity which may subsequently be reamed out and whereby a second reverse movement of said die members and said preform will retract said punches.
 6. An apparatus as claimed in claim 5, further including punch guiding passageways carried by said second die member. 